Spatially-resolved analyses of aerodynamic fallout from a uranium-fueled nuclear test.

Five silicate fallout glass spherules produced in a uranium-fueled, near-surface nuclear test were characterized by secondary ion mass spectrometry, electron probe microanalysis, autoradiography, scanning electron microscopy, and energy-dispersive x-ray spectroscopy. Several samples display compositional heterogeneity suggestive of incomplete mixing between major elements and natural U ((238)U/(235)U = 0.00725) and enriched U. Samples exhibit extreme spatial heterogeneity in U isotopic composition with 0.02 < (235)U/(238)U < 11.84 among all five spherules and 0.02 < (235)U/(238)U < 7.41 within a single spherule. In two spherules, the (235)U/(238)U ratio is correlated with changes in major element composition, suggesting the agglomeration of chemically and isotopically distinct molten precursors. Two samples are nearly homogenous with respect to major element and uranium isotopic composition, suggesting extensive mixing possibly due to experiencing higher temperatures or residing longer in the fireball. Linear correlations between (234)U/(238)U, (235)U/(238)U, and (236)U/(238)U ratios are consistent with a two-component mixing model, which is used to illustrate the extent of mixing between natural and enriched U end members.

When the dust settles: stable xenon isotope constraints on the formation of nuclear fallout.

Nuclear weapons represent one of the most immediate threats of mass destruction. In the event that a procured or developed nuclear weapon is detonated in a populated metropolitan area, timely and accurate nuclear forensic analysis and fallout modeling would be needed to support attribution efforts and hazard assessments. Here we demonstrate that fissiogenic xenon isotopes retained in radioactive fallout generated by a nuclear explosion provide unique constraints on (1) the timescale of fallout formation, (2) chemical fractionation that occurs when fission products and nuclear fuel are incorporated into fallout, and (3) the speciation of fission products in the fireball. Our data suggest that, in near surface nuclear tests, the presence of a significant quantity of metal in a device assembly, combined with a short time allowed for mixing with the ambient atmosphere (seconds), may prevent complete oxidation of fission products prior to their incorporation into fallout. Xenon isotopes thus provide a window into the chemical composition of the fireball in the seconds that follow a nuclear explosion, thereby improving our understanding of the physical and thermo-chemical conditions under which fallout forms.

Improving precision in resonance ionization mass spectrometry: influence of laser bandwidth in uranium isotope ratio measurements.

The use of broad bandwidth lasers with automated feedback control of wavelength was applied to the measurement of (235)U/(238)U ratios by resonance ionization mass spectrometry (RIMS) to decrease laser-induced isotopic fractionation. By broadening the bandwidth of the first laser in a three-color, three-photon ionization process from a bandwidth of 1.8 GHz to about 10 GHz, the variation in sequential relative isotope abundance measurements decreased from 10% to less than 0.5%. This procedure was demonstrated for the direct interrogation of uranium oxide targets with essentially no sample preparation.

Dose from syringe procedures during technetium-99m radiopharmaceutical preparation.

UNLABELLED: We examined the dose from 99mTc contained in syringes and shielded vials to assess in detail the dose burdens in a central pharmacy. METHODS: Absorbed-dose rates at the end of the plunger of a shielded syringe, when 99mTc is contained either in the syringe or in a shielded vial from which the activity would be drawn, were measured with CaF2 dosimeters. The dose rates also were calculated with a Monte Carlo model. RESULTS: When activity was contained in either 3-ml or 10-ml disposable syringes shielded by lead glass, the absorbed-dose rates were 1.35-1.62 mGy hr-1 GBq-1 (5-6 mrad hr-1 mCi-1). When the activity was contained in either a shielded elution or product kit vial, the absorbed-dose rates at the end of the syringe plunger were about 0.40 mGy hr-1 GBq-1 (1.4-1.5 mrad hr-1 mCi-1). These results were reproduced with reasonable accuracy by Monte Carlo simulations. CONCLUSION: The dose burden per unit of activity handled from 99mTc in procedures using syringes is likely to be two to five times larger than the dose burden from calibrating generator eluate. The Monte Carlo simulations suggest that lead K x-rays may be responsible for a significant fraction of the total dose to the fingers and hand of the pharmacist when lead-glass syringe shields are used.

Possible parathyroid imaging using Ga-67 and other aluminum analogs.

Aluminum has been found to localize in parathyroid adenomas, but it has no isotopes suitable for imaging. Chemical analogs of aluminum were therefore evaluated as potential parathyroid seekers. Uptakes of gallium-67, scandium-46 and lutetium-177 were measured in rat parathyroid, thyroid, cervical muscle, and whole blood, over the time period 30 min to 8 days. Both differential and absolute uptakes of Ga-67 and Sc-46 in the parathyroids are greater than that reported for Se-75 selenomethionine. Uptake of Ga-67 is about 2% of the injected dose per gram of parathyroid tissue at 3-4 days, with a parathyroid-to-thyroid uptake ratio of about 6. Studies indicate possible imaging of adenomas at least as small as those now detected only with invasive methods.

Aluminum uptake by the parathyroid glands.

Aluminum-containing drugs are used extensively to bind dietary phosphate and as antacids, but little is known about toxicity and tissue uptake of ingested aluminum. Aluminum concentrations were measured by neutron activation analysis in tissues taken from hyperparathyroid and normal human subjects and from rats. The parathyroid glands contained significantly more aluminum per unit mass than did thyroid or cervical muscle. The concentration of aluminum in the parathyroids appears to be linearly related to dietary aluminum intake.

Direct measurement of osteolysis in man.

Precise, direct measurement of bone calcium release (v(o-)) has been accomplished using a continuous tracer administration (CTA) technique. Dietary calcium (96.97% (40)Ca) is replaced by (40)Ca (99.991% (40)Ca) and blood levels of the naturally occuring isotope (48)Ca are monitored by neutron activation analysis as a function of time. (48)Ca abundance falls as this isotope is excreted and only partially replaced by release from bone. After a suitable period, an asymptotic abundance of (48)Ca in serum, E, is approached which is the fraction of the turnover rate of the rapidly exchangeable calcium pools coming from the skeleton (E = v(o-)/v(t)). E is determined with a standard error of 2%, providing a precise, sensitive index of v(o-). 13 studies in three normal men and one postmenopausal woman receiving maintenance estrogen show large intersubject variations in parameters of calcium metabolism using both CTA and pulse tracer administration (PTA) plus balance techniques. Induced hypercalcemia results in a prolonged decrease in v(o-). Glucocorticoid therapy initially and consistently induces a marked hypercalciuria while effects on most other parameters of calcium kinetics are variable. In two men E fell when testosterone was added to glucocorticoid treatment, consistent with the known antiosteolytic effect of androgens, despite the short period of study.